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GET     /tickets/12    # 查看某个具体的ticket
POST    /tickets       # 新建一个ticket
PUT     /tickets/12    # 更新ticket 12
PATCH   /tickets/12    # 更新ticket 12
DELETE  /tickets/12    # 删除ticekt 12
</code></pre></div><h2 id="http-get-方法"><a href="#http-get-方法" class="header-anchor">#</a> HTTP GET 方法</h2> <p>HTTP GET 方法，用于获取资源，不管调用多少次接口，结果都不会改变，所以是幂等的。</p> <div class="language-text extra-class"><pre class="language-text"><code>GET     /tickets       # 获取ticket列表
GET     /tickets/12    # 查看某个具体的ticket
</code></pre></div><p>只是查询数据，不会影响到资源的变化，因此我们认为它幂等。</p> <p>值得注意，幂等性指的是作用于结果而非资源本身。怎么理解呢？例如，这个 HTTP GET 方法可能会每次得到不同的返回内容，但并不影响资源。</p> <p>可能你会问有这种情况么？当然有咯。例如，我们有一个接口获取当前时间，我们就应该设计成</p> <div class="language-text extra-class"><pre class="language-text"><code>GET     /service_time # 获取服务器当前时间
</code></pre></div><p>它本身不会对资源本身产生影响，因此满足幂等性。</p> <h2 id="http-post-方法"><a href="#http-post-方法" class="header-anchor">#</a> HTTP POST 方法</h2> <p>HTTP POST 方法是一个非幂等方法，因为调用多次，都将产生新的资源。</p> <div class="language-text extra-class"><pre class="language-text"><code>POST    /tickets       # 新建一个ticket
</code></pre></div><p>因为它会对资源本身产生影响，每次调用都会有新的资源产生，因此不满足幂等性。</p> <h2 id="http-put-方法"><a href="#http-put-方法" class="header-anchor">#</a> HTTP PUT 方法</h2> <p>HTTP PUT 方法是不是幂等的呢？我们来看下</p> <div class="language-text extra-class"><pre class="language-text"><code>PUT     /tickets/12    # 更新ticket 12
</code></pre></div><p>因为它直接把实体部分的数据替换到服务器的资源，我们多次调用它，只会产生一次影响，但是有相同结果的 HTTP 方法，所以满足幂等性。</p> <h2 id="http-patch-方法"><a href="#http-patch-方法" class="header-anchor">#</a> HTTP PATCH 方法</h2> <p>HTTP PATCH 方法是非幂等的。HTTP POST 方法和 HTTP PUT 方法可能比较好理解，但是 HTTP PATCH 方法只是更新部分资源，怎么是非幂等的呢?</p> <p>因为，PATCH 提供的实体则需要根据程序或其它协议的定义，解析后在服务器上执行，以此来修改服务器上的资源。换句话说，PATCH 请求是会执行某个程序的，如果重复提交，程序可能执行多次，对服务器上的资源就可能造成额外的影响，这就可以解释它为什么是非幂等的了。</p> <p>可能你还不能理解这点。我们举个例子</p> <div class="language-text extra-class"><pre class="language-text"><code>PATCH   /tickets/12    # 更新ticket 12
</code></pre></div><p>此时，我们服务端对方法的处理是，当调用一次方法，更新部分字段，将这条 ticket 记录的操作记录加一，这次，每次调用的资源是不是变了呢，所以它是有可能是非幂等的操作。</p> <h2 id="http-delete-方法"><a href="#http-delete-方法" class="header-anchor">#</a> HTTP DELETE 方法</h2> <p>HTTP DELETE 方法用于删除资源，会将资源删除。</p> <div class="language-text extra-class"><pre class="language-text"><code>DELETE  /tickets/12    # 删除ticekt 12
</code></pre></div><p>调用一次和多次对资源产生影响是相同的，所以也满足幂等性。</p> <h2 id="如何设计符合幂等性的高质量-restful-api"><a href="#如何设计符合幂等性的高质量-restful-api" class="header-anchor">#</a> 如何设计符合幂等性的高质量 RESTful API</h2> <h2 id="http-get-vs-http-post"><a href="#http-get-vs-http-post" class="header-anchor">#</a> HTTP GET vs HTTP POST</h2> <p>也许，你会想起一个面试题。<strong>HTTP 请求的 GET 与 POST 方式有什么区别？</strong> 你可能会回答到：GET 方式通过 URL 提交数据，数据在 URL 中可以看到；POST 方式，数据放置在 HTML HEADER 内提交。但是，我们现在从 RESTful 的资源角度来看待问题，HTTP GET 方法是幂等的，所以它适合作为查询操作，HTTP POST 方法是非幂等的，所以用来表示新增操作。</p> <p>但是，也有例外，我们有的时候可能需要把查询方法改造成 HTTP POST 方法。比如，超长（1k）的 GET URL 使用 POST 方法来替代，因为 GET 受到 URL 长度的限制。虽然，它不符合幂等性，但是它是一种折中的方案。</p> <h2 id="http-post-vs-http-put"><a href="#http-post-vs-http-put" class="header-anchor">#</a> HTTP POST vs HTTP PUT</h2> <p>对于 HTTP POST 方法和 HTTP PUT 方法，我们一般的理解是 POST 表示创建资源，PUT 表示更新资源。当然，这个是正确的理解。</p> <p>但是，实际上，两个方法都用于创建资源，更为本质的差别是在幂等性。HTTP POST 方法是非幂等，所以用来表示创建资源，HTTP PUT 方法是幂等的，因此表示更新资源更加贴切。</p> <h2 id="http-put-vs-http-patch"><a href="#http-put-vs-http-patch" class="header-anchor">#</a> HTTP PUT vs HTTP PATCH</h2> <p>此时，你看会有另外一个问题。HTTP PUT 方法和 HTTP PATCH 方法，都是用来表述更新资源，它们之间有什么区别呢？我们一般的理解是 PUT 表示更新全部资源，PATCH 表示更新部分资源。首先，这个是我们遵守的第一准则。根据上面的描述，PATCH 方法是非幂等的，因此我们在设计我们服务端的 RESTful API 的时候，也需要考虑。如果，我们想要明确的告诉调用者我们的资源是幂等的，我的设计更倾向于使用 HTTP PUT 方法。</p></div> <footer class="page-edit"><!----> <div class="last-updated"><span class="prefix">上次更新:</span> <span class="time">2021/4/15 上午12:33:56</span></div></footer> <div class="page-nav"><p class="inner"><span class="prev">
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